Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$126.60	8.668%	$137.5737	$137.57	$137.55	$137.60
Purchase #2	$234.65	12.782%	$264.643	$264.64	$264.65	$264.60
Purchase #3	$99.69	3.851%	$103.5291	$103.53	$103.55	$103.50
Purchase #4	$241.55	4.142%	$251.555	$251.56	$251.55	$251.60
Purchase #5	$80.72	10.811%	$89.4466	$89.45	$89.45	$89.40
Purchase #6	$215.39	11.797%	$240.7996	$240.80	$240.80	$240.80
Purchase #7	$80.95	12.465%	$91.0404	$91.04	$91.05	$91.00
7 purchase totals =	$1,079.55		$1,178.5874	$1,178.59	$1,178.60	$1,178.50